It has already been proposed to design the tumblers as disks rotatable about transverse axes and to control their rotation with the aid of magnets carried on the key. According to German Pat. No. 1,553,365, the disks and the housing are provided with complementary formations which permit a rotation of the plug only upon proper alignment thereof with one another. A difficulty inherent in that construction is the fact that the disks must be firmly seated in complementary bores of the plug, in order to resist the pressure exerted thereon when an attempt is made to open the lock with the aid of an improper key or tool, and that consequently the magnetic force must overcome an elevated frictional resistance. Also, intruding dust particles or the like may further impede the rotation of the tumblers. Finally, the large pressures exerted on the tumblers by projections of the housing -- on an attempt to force the lock -- may seriously damage the mechanism and prevent its subsequent response to the use of the proper key.